This invention relates to ophthalmic formulations of cationic, pharmaceutically active agents. The formulations of the present invention are characterized by sustained release of the active agent, and are initially and continually comfortable to the eye. Specifically, the invention relates to formulations of the above characteristics which comprise, inter alia, a basic active and certain cationic exchange resins (finely divided) dispersed in an aqueous solution or gel of an acidic mucomimetic polymer. Such formulations are characterized by controlled cationic-anionic interactions, which appear to be responsible for the resulting comfort and sustained release properties. This invention also relates to methods of treatment which comprise administering the described compositions to the eye.
U.S. Pat. No. 4,911,920, the entire contents of which are incorporated by reference, discloses sustained release formulations for glaucoma therapy, wherein the formulations comprise a basic active and a cationic exchange resin dispersed in an aqueous solution or gel of an acidic, mucomimetic polymer. The cationic-exchange resin in the '920 formulations can be "any pharmaceutical grade cationic exchange resin" (Col. 3, lines 65-66 of the '920 patent) and include the "Amberlite" (Rohm & Haas) and "Dowex" (Dow Chemical Co.) lines of commercially available resins. Examples 2 and 3 of the '920 patent disclose Amberlite IRP-69 resin, a sodium poly(styrenedivinyl benzene) sulfonate having an approximately 8% degree of cross-linking according to its product brochure.